Introduction to the biology and ecology of the freshwater cryophilic dinoflagellate Woloszynskia pascheri causing red ice

The rarely reported red pigmented dinoflagellate, Woloszynskia pascheri, is described from frozen surface waters in Ontario, Canada. New information based on light microscopy (LM) is provided on cell organelles (dinokaryon, chromosomes, pigment droplets and ectoplasmic vesicular layer), the thin-walled ice-bound pellicle cysts and thick-walled summer resting cysts. An earlier published suggestion that W. pascheri has morphology similar to that of Gymnodinium cryophilum (Wedemayer, Wilcox et Graham) G. Hansen et Moestrup is refuted. The process of red ice formation depends on a number of weather-related and other environmental factors. The most important of these being a mid-winter thaw that creates pathways (cracks and melted areas of ice) for passage of swimming cells from the water underlying the ice to water on the surface of the ice. In thin-walled ice-bound pellicle cysts, W. pascheri remained viable at ambient air temperatures lower than -20A degrees C for several days and suggests a unique biochemical physiology that needs research. A summary of the historical classification of this species reveals a tumultuous past and the continuing assignment of this species within the genus Woloszynskia appears doubtful, given the rapidly improving state of knowledge about the fine structure and molecular biology of many other similar species.